Grading seams means trimming seams allowances to different widths. The layers of the fabric in the seam allowance would be cut into tiers. Usually, once one sews a seam, all the layers of the fabric involved would have the same length since they were all sewn with the same seam allowance.
If the fabric used in making a clothing item is heavy or if the seam has many layers, the seam allowance would look bulky. It is the process of making a standard seam into layered tiers of fabric.
Grading seam results in less bulk and a smoother finish from the right side. Although it is a basic technique, doing it makes a finished cloth look professional.
Some tailors and seamstresses are sceptical of grading seams because they have a hunch that it might make the seam weaker than its original form. As long as the cloth would not be laundered almost every day, the graded seam’s strength will remain intact.
What Does Grade a Seam Mean?
In addition to what has been discussed above, grading a seam is trimming it so that it is crisp and flat, instead of having its original bulky shape.
One has to do it by hand so it takes time, especially if the seam being trimmed is long. It is not every time a seam needs to be graded, but it is possible to grade every seam.
However, it is ideal to grade seams of thick fabrics, seams that are pressed together to one side instead of being laid out flat, and seams that are positioned between other layers of clothing as it is on waistbands or top of bags.
How To Grade A Seam
Before you start grading a seam, you have to press it according to the pattern instruction.
If the instruction states that you should press the seam open, then there would not be a need to grade it unless the fabric has many layers. On the flip side, if the pattern instruction says you should press the seam on its side, then you have to grade it.
Once you have pressed the seam, place the seam such that its wrong side is faced upwards so that you can see all the layers you are working with. The layer of the fabric facing you – the one that would be closest to your body when wearing the cloth – will be the shortest.
The one that would be farthest from you when you put on the cloth should be the longest layer. This is so because if placed like this, the longer layer will push the shorter ones into place and act as a cover when one wears the cloth.
Cut the first layer facing you to about 3mm, and every layer that follows it should be trimmed an extra 3mm longer than the one before it.
For example, if there are two layers of fabric, the outermost layer should have 3mm trimmed from it, while the second layer would have 6mm trimmed from it. If the fabric has 3 layers, the layer facing you would be trimmed to 3mm, the second layer 6mm, and the third layer 9mm.
When this is done, the seam should resemble a staircase.
After taking your time to grade the seam, you should press the cloth, take a step back, and admire your hard work. It is worth noting that you can change the measurement of each trim.
They could be more than 3mm or less, it depends on personal preference. The figure given here should act as a guide and should not mean that any other measurement proposed elsewhere is invalid.
How To Grade A Seam On A Curve
Before grading a seam on an inner curve, it has to be clipped so that the seam allowance can spread out and lie flat once when the item is turned. When the seam allowance is laid flat, it has to be clipped at periodic intervals and should end about 3mm from the stitching.
To clip outer curves, they have to be notched so the fabric in the seam allowance can be compressed without producing bulk. Cut small V-shaped notches out of the seam allowance at regular intervals and make sure they end 3mm from the stitching.
Afterwards, grade the seam using the same method explained above. However, when clipping, be extra cautious because if you mistakenly cut into the line of stitching or clip too close to it, you might weaken the seam.